1. Field of the Invention
The present invention relates to a method of manufacturing an electrode used for electrical discharge surface treatment (hereinafter also referred to as an electrical discharge surface treatment-purpose electrode). Further, the present invention relates to a coating formed by electrical discharge surface treatment (hereinafter also referred to as an electrical discharge surface treatment coating), which is formed with use of the relevant electrical discharge surface treatment-purpose electrode.
2. Description of the Background Art
As a method of surface treatment by electrical discharge machining (electrical discharge surface treatment), Japanese Patent Laying-Open No. 05-148615, discloses a method of electrical discharge surface treatment in which a green compact electrode made of fine particles of WC (tungsten carbide) and Co (cobalt) subjected to compression molding is used to form a coating layer having a thickness as large as several tens of millimeters at a surface of a work piece. The coating mainly composed of a carbide such as WC can easily be obtained by subjecting metal to electrical discharge treatment in oil, for example, and thereby allowing the metal to react with carbon in the oil to form the coating.
As a conventional method of manufacturing an electrical discharge surface treatment-purpose electrode to be used in electrical discharge surface treatment, there has been known a method of manufacturing an electrode by molding and heating a metal powder manufactured by a specific granulation method as shown in Japanese Patent Laying-Open No.2005-213560. Specifically, Japanese Patent Laying-Open No. 2005-213560, discloses a method of manufacturing a conductive electrode as follows. Fine metal particles having a mean particle size (diameter) of several tens of micrometers are initially mixed into an organic solvent such as acetone and pulverized with use of a vibration mill or the like to have a mean particle size of at most approximately 3 μm, to prepare a mixture in which the pulverized fine metal particles are dispersed in acetone. To the mixture, approximately 1-10% by mass of wax such as paraffin is added as a binder, to promote propagation of pressure caused by a press to the inside of the metal powder in the subsequent press working. A mixed material made of the above-described mixture and wax is then agitated and sufficiently mixed in a ball mill. Next, a drying device generally referred to as a spray dryer is used to spray the mixed material described above on an atmosphere in which nitrogen at a high temperature is circulated, so as to evaporate the organic solvent and dry the fine metal particles. During the drying, the mixed material is spherically granulated owing to its surface tension, resulting in powder particles having a size of 20 μm-40 μm. The obtained powder is molded by the press, and then heated in a vacuum furnace or in a furnace filled with a nitrogen atmosphere to manufacture the conductive electrode. In Japanese Patent Laying-Open No. 2005-213560,, the wax in the mixed material is molten and removed during the heating.